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(#) Usage of KeyEvent.KEYCODE_BACK

!!! WARNING: Usage of KeyEvent.KEYCODE_BACK
   This is a warning.

Id
:   `GestureBackNavigation`
Summary
:   Usage of KeyEvent.KEYCODE_BACK
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.4.0 (January 2023)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/about/versions/13/features/predictive-back-gesture
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/GestureBackNavDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GestureBackNavDetectorTest.kt)

Starting in Android 13 (API 33+), the handling of back events is moving
to an ahead-of-time callback model. Use
`OnBackInvokedDispatcher.registerOnBackInvokedCallback(...)` and
`onBackInvokedCallback` or AndroidX's `OnBackPressedDispatcher` with an
implemented `onBackPressedCallback` to handle back gestures and key
presses.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/KeyEventKeyCodeBackTest.java:11:Warning: If intercepting
back events, this should be handled through the registration of
callbacks on the window level; Please see
https://developer.android.com/about/versions/13/features/predictive-back-gesture
[GestureBackNavigation]
    if (KeyEvent.KEYCODE_BACK == keyCode) {
        ---------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/AndroidManifest.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="test.pkg"&gt;

    &lt;uses-permission-sdk-33 android:name="foo.bar.BAZ" /&gt;

    &lt;application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:enableOnBackInvokedCallback="true" &gt;
        &lt;activity
            android:name=".KeyEventKeyCodeBackTest"
            android:label="@string/app_name" &gt;
            &lt;intent-filter&gt;
                &lt;action android:name="android.intent.action.MAIN" /&gt;

                &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
            &lt;/intent-filter&gt;
        &lt;/activity&gt;
    &lt;/application&gt;

&lt;/manifest&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/KeyEventKeyCodeBackTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.app.Activity;
import android.content.Context;
import android.view.KeyEvent;

@SuppressWarnings("unused")
public class KeyEventKeyCodeBackTest extends Activity {

    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (KeyEvent.KEYCODE_BACK == keyCode) {
          return true;
        }
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GestureBackNavDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("GestureBackNavigation")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("GestureBackNavigation")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection GestureBackNavigation
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="GestureBackNavigation" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'GestureBackNavigation'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore GestureBackNavigation ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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